First of all try to delete :
delete C:\WINNT\System32\avsmcpa.dll

or

delete C:\WINDOWS\System32\avsmcpa.dll

after that Download McAfee AntiVirus
If you have Windows 2000 Pro
Download Version 4.x (e.g. 4.51) or 6.x (if available)

If you have Windows 95/98/Me/NT
Download Version 5.x

if you gat any error told me
we help to finsh your problme

thanks